a 747 is flying over the pacific when suddenly a cargo door flies open, sucking nine passengers outside a plane. >> it was a typical, normal, calm, serene situation to absolute pandemonium. >> another 747, another terrifying incident. the pilot struggled to control the plane for 32 minutes, but it's hopeless. >> they faced a condition that no pilot could possibly image, which is the airplane is no longer controllable. >> a 737 loses a giant chunk of fuselage mid flight, causing a decompression so powerful it kills a flight attendant. >> i saw what i think was the stewardesses feet as she was sucked out of the plane.

>> a dc10 nose dives and rolls to the ground. >> the entire engine had physically separated from the aircraft. >> all of these disasters have something in common, structures failed with fatal consequences. what pushed these planes to the breaking point? whenever a plane goes down, it's the tragic aftermath that usually flashes over and over again around the globe. scattered wreckage, tattered clues to what may have happened. now, you're about to become an eyewitness to the accident.

our dramatic animations will put you up close and even inside those troubled planes, right next to passengers experiencing unimaginable terror. in the next hour, jets with extreme failures that can be traced back to the machine's very core or structure. >> structural failures when part of the airplane itself fails. in the worst case, it can be a wing actually coming off the airplane or tail section or engine. >> the structure of the airplane is like the bones in your body, and it holds everything together. >> if the airplane structure is the skeleton, then the mechanical parts inside it could be considered the organs. within the structure, the hydraulic system is comparable to muscle, the electrical system like the brain, the pneumatic system like the breath. all three of these systems must be in working order for a plane to fly properly. structural and mechanical failures can often be traced back to the way planes are

maintained or inspected. a textbook example. april 28th, 1988, when a 737 famously lost part of its fuselage in midair. 1:30 pm aloha airlines flight takes off. on its ninth inner island flight of the day. the flight should last just 35 minutes but this 19-year-old boeing 737 has a major problem, growing cracks in its skin that are visible, yet they've gone undetected. patricia aubrey is sitting in row 17. >> we took off, everything was normal. i always read a book when i'm flying. >> to fully understand what's about to happen to aloha flight 243, it's critical to know what

an airplane goes through every time it flies. think of the plane's fuselage as a balloon. every time it goes up, the outside of the plane expands. that's from the cabin being pressurized so people can breathe at high altitudes where the air is thin. when the plane comes down, the skin contracts. every takeoff and landing, no matter how long or short the trip, is considered one cycle. and each cycle puts stress on the airplane, potentially causing microscopic cracks. >> so you have this constant pressure cycle where it expands, contracts, expands and contracts. over a period of time, the metal will eventually start to fatigue because of all of this expansion and contraction just like a balloon. >> as the 737 climbs to 24,000 feet, the cabin pressurizes and the skin on the plane expands, just as it's supposed to. but something else expands, too, those cracks in the 737s

fuselage. suddenly, there's an explosive decompression. its force is so powerful, a flight attendant is sucked out of the plane. >> i saw what i think was the stewardess' feet as she was being sucked out of the plane. magazines, briefcases, shoes, you name it, anything that wasn't tied down was going out that hole. >> an 18-foot section of the plane is gone. passengers sitting nearby can see the sky above and the ocean below. all that's holding the 737 together and just barely are the floor beams and the plane's belly structure. >> about 2 rows in front of me i could see the floor was buckling up, the plane was bending in the middle. >> you can't just have a very strong piece of the bottom of the airplane without having a strong piece of the top. when they lost that crown, it compromised the structural integrity. >> the cockpit would move in one

direction and finally the fuselage would bend and follow it. so it wasn't as though it was a single piece. it actually was bending of the they knew they needed on the ground. >> 243, can you give me your fuel on board? >> 85, 86 plus five. >> roger. how many do you think are injured? >> we have no idea. we couldn't say at this point. >> we'll have ambulance on the way. >> miraculously, the pilots managed to safely land the plane. these images of aloha flight 243 stunned people around the globe. >> it doesn't seem to make any difference how many times we've seen it today, it is still amazing. an airliner with its fuselage ripped away in midair, and all but one aboard survived. it happened over hawaii. >> poof like a balloon explodes and the top came off. >> i saw that the plane was falling apart in the front. i thought we were done.

>> earlier that year, the faa had issued a routine maintenance alert to detect and repair cracks. aloha had not yet repaired problems found on its fleet. when a passenger alerts investigators that she saw a crack, it doesn't take investigators to figure out what's happened to the 737. it's a one-two punch of hot and humid weather and constant ups and downs. >> unlike long haul flights, where you take off at jfk and you fly eight hours and land in london. that's one cycle in an eight-hour period. on these island hoppers, you could fly for two hours and have 20 cycles. up and down, up and down. 30-minute cycles. where you pressurize the airplane, take off, fly for 15 minutes, land. pressurize the airplane again. so the cumulative effect of the cycling of the fuselage is greater in a short period of

time than on a long-haul flight where you have one pressurization cycle in an eight-hour period. that was what was not understood until this particular accident. >> aloha 243 was a case where the industry began to learn the corrosive nature and how carefully it had to be monitored in a marine environment. the airline had spent a decade in and out of the hawaiian islands. the corrosion had expanded and with it, cracks. the cracks began to propagate and move, and they finally failed. the results were absolutely catastrophic. when we come back, the deadliest plane crash in the history of u.s. aviation as a five ton engine violently rips away from a dc-10 on takeoff. >> the pilots knew they had a serious problem, they knew the engine had failed, they didn't know it had actually come off the airplane. and a night flight over the pacific goes treacherously wrong. >> in one second passengers were

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we've seen how airplane failures, whether structural or mechanical, can often be traced back to the way planes are maintained or inspected. a tragic case in point, american airlines flight 191, the deadliest single airplane crash on u.s. soil. may 25th, 1979, the friday of memorial day weekend. american flight 191, a mcdonnell-douglas dc-10 is on its way to los angeles from chicago's o'hare airport. with 258 passengers and 13 crew members on board. melody smith and kim jockal's parents are on the first leg of a trip to hawaii.

>> my mom and dad always had a big kickoff for summer. we normally would have been with them. however, they decided about six months before that they were going to hawaii. >> a few minutes before 3:00 p.m., the plane is cleared to taxi to runway 32 right. at 3:02 p.m., it's cleared for takeoff. our investigative animations are about to turn you into an eyewitness to a horrific accident. >> the flight crew, flight 191 starts their normal takeoff. as the airplane departs the runway on the normal climbout, they get the indication that they have an engine failure. >> one of the dc-10's engines has ripped away from the plane, flying up and over the left wing. gone with it are hydraulics and pneumatics, systems critical to controlling the airplane. >> the pilots knew they had a serious problem.

they knew the engine had failed, but they didn't know it had come off the airplane. there's no indication for that. >> look at this, look at this. blew up engine. equipment. >> the leading edge slats which give the wing better lift during slow speeds during takeoff and landing are controlled hydraulically. now with no hydraulics on the left side, the slats retract back into the wing. >> which means he has less lift on that side than he had on the opposite side, so it wants to roll. >> an eyewitness manages to snap a photo of the plane rolling on to its side with its left wing pointing straight down to the ground. what happens next seals the fate of flight 191. >> pilots are trained to handle engine failures, and they did what their training taught them to do. they reduced their air speed. >> but when they did that, they no longer had control across the flight controls. >> they just didn't have enough

time to do it. >> the plane staggers up to 325 feet. as it's rolled on to its side and slowed down, it's uncontrollable, and goes into a nosedive opinion. >> american 191, heavy. want to come back into what runway? >> he's not talkin' to me. >> there he goes. there he goes. >> within 31 seconds of the engine severing from the plane, the dc-10 slams into a trailer park less than a mile from the runway. >> the entire flight has lasted just two minutes, but changed these sisters lives forever. >> i remember you saying, there's no other way to tell you, there's been a really bad accident. >> yeah, and mom and dad are dead. >> mom and dad are dead. >> i said, you need to find a way to come hope. >> there was no noise at all, it

went right into the ground. everything in its path was blown into a sheet of flame. >> initially, ntsb investigators are baffled what could have caused a failure of this magnitude. >> this is all that's left of american airlines flight 191, as far as it got on its way to los angeles. >> they sift through the wreckage and look to the plane's two flight recorders for clues. within days of the crash, it began to zero in on a part called the pylon. it has a 13-inch crack they believe was caused by fatigue prior to the crash, which maintenance inspections had missed. what exactly is a pylon? aviation consultant john cox showed us at evergreen international, an airplane maintenance and storage facility outside tucson, arizona. >> you can see the pylon assembly, on which the engine rests on the pylon and it's attached to the wing.

>> it looks like an arm that the engine is hanging off of. that's a very complex piece of structure. it has to be designed to take a heck of a load from the engines. >> investigators also scrutinize the plane's service history. that's where the puzzle pieces start to come together. it turns out not to be a design flaw. it's a troubling maintenance practice. >> the whole issue of the accident centered on the maintenance practice of changing an engine with this pylon attached as opposed to the more correct and approved procedure, which is to take the pylon away from the engine while attached to the airplane. >> the manufacturer recommending detaching the engine to the pylon, but leaving the pylon attached to the wing. at the time, engineers from several airlines were using a shortcut. they found if the pylon and engine were removed in one piece, they could change the engine more quickly. >> they just dropped the entire

unit from the wing. they could change the component, put it all back together. in theory it sounded great, on paper it looked good. >> it's when maintenance workers are reattaching the engine and the soon to be fatal mistake is made. if the airline had followed manufacturer requirements, workers would have simply reattached the engine to the pylon using a specialized machine, recommended by the manufacturer. but because they've removed the massive engine/pylon assembly together, now it has to be replaced as one unit. using a forklift, workers inadvertently crack the top section of the pylon called the flange as they try to fit the assembly back on to the plane. >> because they were using a forklift to try to hold this heavy engine up while they put these two big bolts in place to hold the pylon on the wing, they created a stress situation that, over a period of time when the

airplane was returned to service, caused one of the bolts to fail. >> this morning, investigators were out on runway 32 right at o'hare airport looking for a bolt about four inches long. >> the crack is hidden from view, so it goes undetected. with every takeoff and landing cycle, putting stress on the broken flange, the crack is growing, and no one knows it. eight weeks after the engine change when flight 191 takes off on that warm spring afternoon, suddenly, without warning, disaster. >> takeoff is when this engine's producing the most thrust when there's the most force on the pylon is during takeoff. if it were going to fail, makes absolutely perfect sense it would fail shortly after takeoff. >> as flight 191 starts to lift off at the end of the runway, the cracked flange fails. ripping the engine away, and taking with it a portion of the

left wing's leading edge, which causes a loss of hydraulic fluid. as a result, the left wing slats retract, the left wing loses lift, and the rest sadly is history. >> when our parents died initially, we would have all of their friends, a lot of friends saying, well, isn't this wonderful, they went together. >> they went together and they were so young. >> and they loved one another and whatever. and i can remember at the time i had to kind of choke back saying, no, i don't think this is wonderful. >> seven months after the accident the ntsb issues several critical and immediate recommendations for airlines. among them, airlines must discontinue the unapproved maintenance practice and inspect pylon attach points on all dc-10s by approved inspection methods. the ntsb also recommends airlines change their flight manuals. so pilots know not to reduce speed in such a scenario as in the case of flight 191.

neither american airlines or mcdonnell-douglas admitted fault to this accident. but in april 1991, the two companies agreed to share the costs of settlements in more than 200 lawsuits that were filed. the terms of those settlements remain confidential. >> every accident and incident, because of its unique characteristics, we are going to learn something. we have to heed those lessons. we've got to heed them and we have to enhance aviation safety. we don't want those people to have died in vain. coming up next, the cargo door where your luggage goes. imagine it opening in midair. our dramatic animations put you at the scene of another structural heart stopping failure. >> i denied it. complete, absolute mental denial. this is not happening. and a plane flying out of control crashes into a mountain. we'll take you deep inside this

747 to discover what went wrong. >> that would be a nightmare scenario for a pilot. in here, the planned combination of at&t and t-mobile would deliver our next generation mobile broadband experience to 55 million more americans, many in small towns and rural communities, giving them a new choice. we'll deliver better service, with thousands of new cell sites... for greater access to all the things you want, whenever you want them. it's the at&t network... and what's possible in here is almost impossible to say.

flying requires trust that all the people involved, ground crews, mechanics, pilots are doing what they're supposed to do. and that the airplane itself will function normally. but for the passengers of this unlucky flight, that trust is about to be shaken, when a cargo door explodes open in midair. >> 1989, i was a practicing trial lawyer in denver. i hadn't had a vacation in about three years. >> bruce lambert is a licensed pilot and an aviation attorney who represents plane crash victims. he never imagined he would end up experiencing and surviving a deadly incident in the sky. >> i had just completed working extensively on northwest 255, a crash in detroit, michigan.

i was about to get started on a new case, continental 1713 in denver, colorado and i had a three-week break in between those two cases. this was going to be a vacation i would really remember. >> february 24th, 1989, 2:00 a.m., united airlines flight 811 is en route from honolulu to auckland, new zealand. 355 people are on board for the night flight over the pacific. takeoff and initial climb are normal. y >> we were settling in for a restful flight, and the aircraft was climbing. >> but as the boeing 747 approaches 23,000 feet, the shock of a lifetime. >> there was an explosion. everything that wasn't tied down was airborne. >> these dramatic animations put you next to the plane as the forward right cargo door rips open in flight, slams upward

creating a gaping hole in the fuselage and then falls from the plane. the resulting massive depressurization sucks out two rows of seats and nine passengers. >> the door swung out, it's an outward opening door, and there's a spot that keeps it from going up all the way. in flight, the air loads were such that it kept going above that slot. it went all the way up and slammed against the fuselage above the door and actually fractured that fuselage above the door. >> in one second our fellow passengers were sitting there with magazines and drinks, with their reading lights on and then a nanosecond later they were gone. >> the structural integrity of the main deck has failed extensively. there's a 10x15 foot hole in the fuselage and debris has been sucked into both engines on that side. the number three engine is

pulsing fire, number four is also failing. the pilot begins a rapid descent to where passengers can breathe normally. >> they declared an emergency, and en route back to the airport they literally had to shut down both the number three and mum four engines so now they're flying this big aircraft on two engines. that, in and of itself, is a challenge for any pilot. >> for some passengers, it's a moment of terror. someone in business class manages to nap this photo as the plane is quickly descending. >> you know, everyone likes to think that in a stressful situation that you will act properly, you will act heroically, that you will do the right thing. but when you can do nothing, there's no place to go. there's no place to run. you can't scream, because no one can hear you. so, what do you do? you sit there with your hands

folded in your lap and you look at the people around you. and there is very little comfort from watching others, who are experiencing the same threat that you are. >> then out of nowhere, there's a sudden glimmer of hope. >> i remember seeing a number of the passengers on the right side pointing to the windows. and if you looked out the window, you could see there were lights. they were the lights of honolulu, lights of hawaii, and we could see land. >> after 20 nerve-racking minutes, united flight 811 touches down in honolulu. >> a cheer, like a roller coaster ride, and hands were thrown up above their heads as everybody exclaimed their joy that the airplane had touched down. >> this photograph was taken during the evacuation. 346 surviving passengers and crew get off the plane within one minute. >> people say, how in the world could everybody get off that quick.

i tell them, we had a very highly motivated group of people. >> a grinding noise woke me up. it was a bang and a flash. i looked up, the whole right-hand side of the business compartment had gone. >> the sound of the explosion, the feeling of the explosion and the violence of the explosion is awesome. and i hope none of you have to go through it. >> it's a tragedy for the families of the nine passengers who don't survive. and a trauma for the rest. but at least it's over. but for investigators, the story is just beginning. they see that the cargo door is missing. what they don't know is why did it open in flight. when we return, the cargo door is a key piece of evidence. how will investigators find it in the middle of the pacific ocean?

>> where was it? it doesn't have a beacon, it doesn't have a transponder. and more deadly crashes. our animations put you front and center. >> the airplane became less and less controllable to the point where it was no longer controllable at all. an accident doesn't have to slow you down. with better car replacement, available only with liberty mutual auto insurance, if your car is totaled, we give you the money for a car one model year newer. to learn more, visit us today. responsibility. what's your policy? this past year alone there was a 93% increase in cyber attacks. in financial transactions... on devices... in social interactions... and applications in the cloud. some companies are worried.

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here's what's happening. debt ceiling deals may be on the way after talks with republican leaders and the white house broke down. john boehner said he is working on one solution wheen senate democrats are considering offering their own legislationing? the lady accusing strauss-kahn of assault is going public. the woman stands by her story that she was attacked by the former head of the imf. now back it "why planes crash."

when any structural element of an airplane fails, the result can be fatal. a 747 has a cargo door blown out in mid flight. the decompression is so powerful it sucks two rows of seats and nine passengers out of the plane in a split second. >> this was taken from row 17 aisle seat. >> this video shot by bruce lambert two weeks after the fatal accident documents the aftermath of united airlines flight 811. investigators immediately know the problem centers on the cargo door. they can tell from the gaping hole where it used to be. the key question, why did it explode open, plummeting to the pacific ocean below? but the key piece investigators would like to examine, the cargo door itself, is lost at sea.

with no hard evidence, the ntsb issues a report 14 months after the accident. based on previous problems with other 747 cargo doors, the report mentions a possible electrical malfunction in the cargo door locking mechanisms. >> falling out of the ceiling. >> but aviation inspectors recall most of the blame falling on the honolulu airport ground crew. >> it's one of the most interesting stories in aviation accident investigation, because initially it was thought that the people closing the door had not done it properly and the door had not been sealed and latched properly. >> a number of employees that work for the airline had come forward after the problem saying, of all the individuals that work in honolulu, this person was the least likely to not close the door properly. he was known for being very meticulous. but absent any physical evidence to the contrary, the ntsb is bound by facts.

and the best estimate of facts at that time said he didn't close the door properly. >> is it human error or is there another explanation? >> it wasn't until a year and a half later when the navy went down and actually found the cargo door, the two pieces of the cargo door, brought them back up and they were examined. the real cause or the true cause of the event was identified. >> to follow the cargo door failure on united flight 811, it's important to understand the two-snap locking system that secures 747 cargo doors. first, a series of c-shaped latches electronically rotates around pins in the bottom of the door frame. then for further reinforcement a handle moves l-shaped arms up against the c-latches to keep them in place. in addition, there are pins up and down both sides of the door.

normally all of this holds the door shut. in the case of united flight 811, something goes horribly wrong. >> forensic analysis of the door indicated that there was actually a short circuit. >> it's an electrical problem that had caused unexpectedly a command to unlock the door, to actually come open. so that it was a design issue. >> finding that cargo door was critical to answering this question, obviously. >> it was so critical that the ntsb actually reissued the report with a different and more up to date cause as well as causing all 747s to be redesigned to prevent this kind of failure from occurring again. it was a case where the industry learned a very valuable lesson. >> the final cause, according to the ntsb, faulty wiring that allowed the properly closed door to unlatch, some time between the closing of the door and takeoff.

in other words, it happened on the ground, but the ground crew didn't do it. before this accident, there were several other documented cases of electrical problems with cargo doors on 747s. in fact, boeing had alerted airlines to the problem, and the faa had given airlines nearly two years to perform the $2,000 per door upgrade at the airline's expense. when united 811 took off on february 24th, 1989 the deadline was a year away, and the problem was scheduled to be corrected by united two months after the accident. to this day, that angers passenger dick gutschall. seat 7c. >> there was a warning out by the faa that that door had a problem. united chose not to correct it. that's the only thing that really bothered me, because i still fly united.

they made a mistake there, they did not fix the problem when they could have fixed it. >> aviation attorney bruce lambert ended up representing 40 of his fellow passengers in lawsuits against united. without admitting any wrongdoing, the airline did settle lawsuits for millions of dollars. >> as i told the lawyers for united, i would much prefer getting on an airplane where nothing happens and have no cases than being on an airplane that blows up at 23,000 feet and represent my fellow passengers. i'll make a deal with any airline i fly on. you get me there safely and i won't represent any passengers. when we come back, a catastrophic case of structural failure.

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as we've seen, structural failure on airplanes can be caused by inadequate inspections, faulty maintenance practices or design flaws buried deep within the guts of these giant machines. but the deadliest single plane crash in history, a 747 that crashed into a japanese mountainside had another cause entirely. august 12th, 1985, japan airlines flight 123 has a staggering 524 people on board. the plane is set to fly from tokyo to osaka. this workhorse of a jet makes the one-hour trip several times a day. it's like flying from new york to boston. susan's boyfriend is on board.

>> aki was a banker, he was traveling on business that day. it was a very humid, hot, japanese summer day. from the moment i opened my eyes that day, and aki did too, there was a hint of something wrong, which i couldn't explain. >> also on board, takashi's sister, sumako. >> she did tell me she's going to tokyo. i said to her, it's dangerous to fly. she told me, don't worry, brother, i've already bought a ticket. >> you're looking at footage of the actual plane involved in this crash, taking off on its final ill-fated flight. 6:12 p.m., everything seems normal as the plane lifts off and climbs out. suddenly, 12 minutes into the flight, there's a problem.

>> they were in the middle 20,000 feet, which is where airplanes experience the most pressure on the vessel itself. at that point they received a door warning that a door was ajar which turned out not to be the case. >> we've already seen how an airplane's fuselage expands as the plane goes up and contracts as the plane comes down. the altitude with the greatest pressure differential between the pressurized inside of an aircraft and the unpressurized atmosphere outside is right around 24,000 feet. that's where jal-123 experiences an explosive shock. >> a massive decompression for reasons that they didn't know. but the crew did not realize the amount of damage they sustained until very quickly, the airplane became less and less controllable to the point it was no longer controllable at all. that would be a nightmare scenario for a pilot. >> what the pilot's don't know is that a critical piece of the

747 structure has cracked and expanded to the breaking point that it snapped. it's the aft pressure bulkhead, an umbrella-shaped structure toward the back of the plane. >> it's the device that keeps the pressure in the back part of the airplane contained properly. without that pressure, you can't pressurize the two and you wouldn't be able to breathe at 35,000 feet without the use of pressurized supplemental oxygen. >> the back of the airplane is getting a considerable amount of stress, not only from the pressurization, but also from the tail and all the stresses of flight. that bulkhead is very, very robust. it is a serious piece of structure. >> at the moment of the decompression, all the pressurized air for the cabin needs somewhere to go. it blasts back the cracked bulkhead, and unbeknownst to the pilot, the tremendous force blows the vertical fin and other parts of the tail section right off the giant 747.

critical hydraulic lines are severed in the process. >> the first officer makes several radio calls that says, we're in uncontrollable flight, we do not have control of the airplane. they're fighting literally for their lives. >> the airplane starts to go into what they call a pitch oscillation, up and down, as well as a dutch roll. the airplane starts to swing back and forth. and no matter what the pilot tries to do as far as flight control inputs, he's not having an effect. >> the pilots fight desperately for control of the airplane for 32 terrifying minutes. they manage to keep the plane aloft, but with no hydraulics, they can't control the plane's up and down or side to side

movement. eyewitnesses on the ground later report that the plane was flying like a, quote, staggering drunk. the plane goes into a nosedive, falling 18,000 feet a minute. just before 7:00 p.m., jal flight 123 drops off the radar screen. it has slammed into a mountain at nearly 400 miles an hour. >> these are the first daylight pictures from the sight of what appears to be the worst single airline crash ever. a 747 has gone down. it's believed that all 524 people on board were killed. coming up next, investigators face together the grim task of piecing together the mystery. >> we had a catastrophic scene, we have millions of airplane parts scattered over the mountain side. >> but among the wreckage a miraculous discovery. o the test against the speed of a rescue unit. go !

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japan airlines flight 123. it's a tragedy with many clues tonight, but no hard answers yet. >> it takes rescuers to get to where the flight slammed into a mountain northwest of tokyo. when investigators finally reached the crash site, they began to comb the wreckage for clues. they find something they did not expect. two women and two young girls have survived. the four people that survived the accident were in the aft part of the airplane. it was thrown well away from the impact point. >> this man hoped his sister would be among the survivors,

sadly he discovered at a makeshift morgue that was not the case. >> she only had a scar here on the chin. there was no damage to the rest of the body. i recognized her right away. >> testimony from those that did survive later proved valuable, but meantime there was countless other things to pursue. >> we had literally millions of pieces of plane to gather over the mountainside. all of these different sources of information help the investigators put the puzzle together. within days, a photograph taken by a villager taken from over the village. part of the missing tail section, including the vertical fin which keeps the plane stable is fished out of a bay, 100

miles away from the mountain. >> it was a distance from the crash site. they knew it departed the plane early. so now you ask the question, what could cause a decompression, control problems and the loss of a vertical fin. >> looking at the plane's maintenance history, they learn there was previous damage to the aft brusher bulk head, and that's what keeps the cabin pressurized. it was cracked seven years before the crash. when the tail was accidentally drug along the runway, something known as a tail strike. >> it can occur in one of phases of flight. it can occur on takeoff or on landing, when the plane is in a tail low and nose high attitude, and either way it will create damage. >> the repair is problematic. the structure is so large, more than 15 feet across, the airplane was originally built

around it. to make the fix, boeing removes the skin of the airplane around the bulk head, replaces the bullhe bullhead's damaged half and then replaces the skin over it. now the trouble, to fuse the havs it called for a single slice plate or double lure, and the doubler doesn't fit. they cut the piece in half. that's problem number one. problem number two, the correct procedure calls for two rose of rivets to hole the doubler in place, and only one row is placed on there. >> they decided to alter the installation procedure. it was not an approved procedure. >> the repair is certificated to

last 10,000 takeoffs. this plane had gone more than 12,000 cycles. because a sealant has been used, cracks developing between the rivets are not found. this plane is a ticking time bomb. >> unfortunately, the repair was insufficient and cracks started to develop after the plane was returned to passenger use. there was no proper inspection procedure as well. >> cracks began to connect between the rivets, leading the bulk head to fail catastrophically. it was a structural failure due to a faulty repair and inadequate oversight. >> when we look back at structural failures, how common is it that it's remain or

maintenance related? >> i think we're finding more and more where it's repair latd. >> there was two suicides in the wake of the incident. a japan airlines employee, who was working with victims' family, and an inspection engineer who issued a certificate of airworthiness after the 1978 tail strike. to this day, jal 123 remains the deadliest single crash in the history of aviation. we have seen the disasters as a result of aircraft not properly maintained or inspected. american flight 191, aloha 293. and then we have seen what happens in a design flaw. those flights are the exception and not the rule.

every day, 3 million passengers do land safely. >> i am asked often what is the most dangerous part of flying, and literally it's driving to the airport. >> and those kinds of statistics are of little comfort, and they have seen and felt the consequences of structural failure firsthand. >> we have manufactures in making incredible machines, cars, elevators, airplanes, trains, and when you get on these elevators and trains, and these airplanes, you expect them to work. but once that faith in machines is shaken, you have this cynical thought, you know, the question authority bumper sticker, i suggest one, question technology, and put it on your suitcase.